Effect of ultrasound irradiation and Ni-loading on properties and performance of CeO2-doped Ni/clinoptilolite nanocatalyst used in polluted air treatment

In this research nanocatalysts containing 5, 10 and 15 wt.% of Ni, dispersed by sonication over CeO₂–clinoptilolite composite support were compared toward total oxidation of toluene. Their catalytic performance at different temperatures between 150 and 350 °C was studied based on the oxidative destruction of toluene. The results indicated that the activity of Ni/CeO₂–clinoptilolite nanocatalyst for toluene oxidation increased from 33 to 44% at 250 °C by employing sonochemical method in synthesis of catalyst. Meanwhile, the catalytic activity was also improved when Ni content was increased from 5 to 10 and 15 wt.%. With the aid of several characterization techniques like XRD, FESEM, PSD, EDX, BET and FTIR, the correlation between nanocatalyst structure and its activity was addressed. It is indicated that sonochemical method can lift the catalytic activity due to the better dispersion of catalyst active components and also higher surface area. Among sonicated samples, 15 wt.% Ni nanocatalyst showed the highest toluene oxidation due to the better dispersion of catalyst active components and hence to more effective catalytic sites.     

Mesoporous simonkolleite–TiO2 nanostructured composite for simultaneous photocatalytic hydrogen production and dye decontamination

In the present work, mesoporous simonkolleite–TiO₂ composite was prepared with sol–gel method. The composite photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and Raman spectroscopy. Also, surface area and particle size were analyzed using BET equation. The photocatalytic hydrogen production with simultaneous decolorization of Remazole Red (F3B) dye was investigated over TiO₂ and simonkolleite–TiO₂ composite under UV–vis light irradiation. It was worthy to be noted that the rate of hydrogen production over simonkolleite–TiO₂ is higher that produced over TiO₂. The maximum amount of photocatalytic-produced hydrogen was 2.1 mmol and 3.3 mmol within 240 min using TiO₂ and simonkolleite–TiO₂ composite, respectively. The specific production rate of hydrogen from photocatalytic conversion of dye was calculated. Improvement of apparent quantum yield (22.07%) after 5 h was achieved upon addition of simonkolleite to TiO₂. This high apparent quantum yield proves that the system proposed in this study could be a hopeful approach toward using sunlight energy as outlook energy source. The obtained results suggested that a new process for H₂ production from wastewater could be achieved. The process also provides a method for degradation of organic pollutants with simultaneous H₂ production.     

Simultaneous photocatalytic treatment of Cr(VI), Ni(II) and SDBS in aqueous solutions: Evaluation of removal efficiency and energy consumption

Simultaneous photocatalytic reduction of poisonous Cr(VI) and Ni(II) ions, coupled with photocatalytic oxidation of sodium dodecyl benzene sulfonate (SDBS) were studied with a trace amount of commercial titania nanoparticles and by means of a direct-photo-irradiation reactor. The co-presence of metal ions and SDBS causes metal ions reduction as well as SDBS oxidation to enhance and energy efficiency to improve. XRD, XPS and FTIR analysis were used to characterize TiO₂ particles before and after usage with the aim of evaluating the mechanism of reactions. The effect of major operating parameters, pH and temperature, was investigated. Under conditions of [Cr(VI)]₀ = [Ni(II)]₀ = 5 mg/L, [SDBS]₀ = 10 mg/L, [TiO₂] = 40 mg/L, pH 6 and T = 35 °C; the removal efficiencies of 55.4%, 71.2% and 57.2% were obtained, respectively, for Cr(VI) and Ni(II) reduction, as well as for SDBS oxidation, after 110 min operation. The relevant kinetic model jointed with the Arrhenius equation was introduced. Pseudo-first-order reactions are relevant. Energy consumption (electrical and thermal) evaluations revealed that operations at higher temperatures provide significant cost reduction. Meantime, a criterion was proposed for a consistent assessment of this kind of processes.     

Disintegration of waste activated sludge by different applications of Fenton process

Oxidative disintegration of municipal waste activated sludge (WAS) using conventional Fenton (Fe²⁺ + H₂O₂, CFP) and Fenton type (Fe⁰ + H₂O₂, FTP) processes was investigated and compared in terms of the efficiency of sludge disintegration and enhancement of anaerobic biodegradability. The influences of different operational variables namely sludge pH, initial concentration of Fe²⁺ or Fe⁰, and H₂O₂ were studied in detail. The optimum conditions have been found as catalyst iron dosage = 4 g/kg TS, H₂O₂ dosage = 40 g/kg TS and pH = 3 within 1 h oxidation period for both CFP and FTP. Kinetics studies were performed under optimal conditions. It was determined that the sludge disintegration was happened in two stages by both processes: rapid and subsequent slow disintegration stages and rapid sludge disintegration stage can be described by a zero-order kinetic model. The effects of oxidative sludge disintegration under the optimum conditions on anaerobic digestion were experienced with biochemical methane potential (BMP) assay in batch anaerobic reactors. Total methane production in the CFP and FTP pre-treated reactors increased by 26.9% and 38.0%, relative to the untreated reactor (digested the raw WAS). Furthermore, the total chemical oxygen demand reductions in the pre-treated reactors were improved as well.     

Use of advance oxidation process to improve the biodegradability of olive oil mill effluents

In this study, recalcitrant total phenol (TPh) and organic matter removal were investigated at olive mill wastewater (OMW) in sequential Coagulation and Fenton system. This study focused on different operational parameters such as pH, H₂O₂, and Fe²⁺ dosages, and [Fe²⁺]/[H₂O₂] ratios. The optimum conditions were determined as; pH = 3; [Fe²⁺] = 2.5 g/L; [Fe²⁺]/[H₂O₂] = 2.5. A higher treatment efficiency was achieved at sequential Coagulation and Fenton system (COD, 65.5%) and TPh, 87.2%), compared to coagulation process (COD, 51.4%; total organic carbon (TOC), 38.6% and total nitrogen (TN) 52.1%). This study demonstrated that the Coagulation and Fenton process has a potential for efficient removal of phenolic pollutants from wastewater.     

Adsorptive removal of basic dyes from aqueous solutions by surfactant modified bentonite clay (organoclay): Kinetic and competitive adsorption isotherm

Cationic surfactant (Hexadecyltrimenthylammonium chloride) modified bentonite clay was prepared and systematically studied for its adsorption behavior as an efficient adsorbent for the removal of basic dyes such as methylene blue (MB), crystal violet (CV) and Rhodamine B (RB) from aqueous phase. Organo modified clay shows better capacity for the removal of three dyes. The adsorption process was found to be dependent on pH and initial dye concentration. The maximum dye sorption was found to be at a pH of 9.0 (99.99% for MB, 95.0% for CV and 83.0% for RB). The adsorption capacity for the dyes was found to be 399.74, 365.11 and 324.36 μmol/g for MB, CV and RB, respectively at 30 °C. The equilibrium uptake was attained within 240 min. The kinetic studies were revealed that sorption follows a pseudo-second-order kinetic model which indicates chemisorption between adsorbent and adsorbate molecules. Adsorption isotherm indicates non-energetically adsorption sites which fit with Freundlich isotherm model. The fitness of kinetics and isotherm models was evaluated by using HYBRID error analysis function. Competitive adsorptions of dyes were studied by using binary component systems.     

Effects of applied voltage on hydrogen production rate of a single reactor BML with Clostridium sp.

This study aimed to explore the influences of single-chamber systems with different applied voltage on bio-hydrogen (H₂) production. The reactor used was the bio-electrochemically assisted microbial reactor (BEAMR) membrane-less (BEAMR-membrane-less, BML). The microbial dark fermentative H₂ production method was adopted. After the hot screening process and the DNA sequencing, the domesticated dominant microflora was Clostridium sp. This study discussed the influences of the cases with (continuous and intermittent) and without applied voltage separately. The results showed that, the H₂ production rate of the case with intermittent applied voltage (117 mL/h g VSS) of 0.24 V was increased of 1.7 folds higher than the without applied voltage (69 mL/h g VSS) and 1.3 folds higher than the case with continuous applied voltage (88.2 mL/h g VSS) of 0.24 V. The produced H₂ concentration with intermittent applied voltage was 18.9% (18.6–19.1%) higher than the without applied voltage, while there was no significant difference with continuous applied voltage.     

Effect of solvent on the hydrothermal liquefaction of macro algae Ulva fasciata

Hydrothermal liquefaction is an attractive approach for the conversion of aquatic biomass like algae as it does not require the energy intensive drying steps. The objective of the study is to understand the effect of various solvents (H₂O, CH₃OH and C₂H₅OH) on product distribution and nature of products of hydrothermal liquefaction of macro algae Ulva fasciata (MAUF). Hydrothermal liquefaction of MAUF was performed using subcritical H₂O (300 °C) as well as supercritical organic solvents CH₃OH and C₂H₅OH (300 °C). The use of alcoholic solvents significantly increased the bio-oil yield. The bio-oil yield was 44% and 40% in case of liquefaction with CH₃OH and C₂H₅OH respectively whereas the bio-oil yield was 11% with H₂O. Use of alcoholic solvents converted the acids obtained in bio-oil to the corresponding methyl and ethyl esters. ¹H NMR data showed that use of alcoholic solvents (C₂H₅OH and CH₃OH) increased aliphatic content of bio-oil1 (ether/methanol/ethanol fraction). FTIR and SEM results showed the difference in the bio residue obtained using alcoholic solvents and H₂O. The results showed that liquefaction with supercritical alcohols is an effective way to produce functional hydrocarbons for chemical feedstock.     

Calorimetric behaviors of N2H4 by DSC and superCRC

The objective of this study is to obtain information about the thermal decomposition behaviors of hydrazine (N₂H₄) caused by metals, using differential scanning calorimeter (DSC) and SuperCRC. The DSC measurements revealed that the exothermic reactions of N₂H₄ were caused by the reaction conditions such as the type of cells; the T_DSC with a gold pan is 485.2 K and that with a glass capillary is 620.5 K. Besides, the activation energy of the thermal decomposition of N₂H₄, calculated from the Kissinger and Ozawa methods, were found to be about 38±2 kJ mol⁻¹ in the gold pan and 141±8 kJ mol⁻¹ in the glass capillary. Moreover, a heat flow profile was observed with SuperCRC during the mixing of N₂H₄ and the metal ion solution at 298 K. The maximum heat flow was related to the metal ion oxidative characters. The higher oxidative characters would provide a faster acceleration for the exothermic behavior than the lower oxidative ions. Based on this study, Mn(VII) and Cr(VI) were considered to exhibit strongly oxidative characteristics during mixing with N₂H₄.     

Evaluating the efficacy of alumina/carbon nanotube hybrid adsorbents in removing Azo Reactive Red 198 and Blue 19 dyes from aqueous solutions

Concerning the high volume of wastewater containing dye in Iran and its adverse effects, it is necessary to develop scientific solutions for treating these wastewaters. The aim of this study was to evaluate the efficiency of the alumina-coated multi-walled carbon nanotubes in removing the Reactive Red 198 (RR 198) and Blue 19 (RB 19) dyes. Synthetic samples including dye with different concentrations were prepared. These samples were put in contact with different contents of alumina/multi-walled carbon nanotubes, in different pH values, in different contact times, different temperatures and the presence of sodium sulfate or sodium carbonate. The optimum pH, dye concentration and temperature for removal of the two dyes was 3, 50 mg l⁻¹ and 25 °C, respectively. The optimum adsorbent dose for removal the RR 198 dye was 0.5 g l⁻¹ and for Blue 19 was 0.4 g l⁻¹. The optimum contact time for RR 198 was 150 min and RB 19 was 180 min. In this condition, maximum removal efficiency for RR 198 and RB 19 was 91.54% and 93.51%, respectively. The adsorption study was analyzed kinetically, and the results revealed that the adsorption fitted a pseudo-second order kinetic model. According to these results alumina/multi-walled carbon nanotubes can effectively remove RR 198 and RB 19 from aqueous solutions.     

Removal of H2S by co-immobilized bacteria and fungi biocatalysts in a bio-trickling filter

Biological control of odor gases has gained more attention in recent years. In this study, removal performance of a vertical bio-trickling filter inoculated with bacteria and fungi was studied. Bacteria and fungi were isolated from activated sludge in a sewage treatment plant. By adopting “three step immobilization method”, the bio-trickling filter could degrade pollutant immediately once hydrogen sulfide (H₂S) passed. The optimal empty bed resident time was 20 s. The optimal elimination capacity was about 60 g H₂S m^?3 h^?1 with removal efficiency of 95%. And the maximum elimination capacity was 170 g H₂S m^?3 h^?1. Pressure drop was ranged between 5 and 15 mm H₂O per bed over the whole operation. Removal efficiency was not affected obviously after terminating nutrient supply. The bio-trickling filter could recover back after shut down H₂S gaseous and liquid supplies simultaneously. Microbial community structure in the bio-trickling filter was not changed significantly.Combining bacteria and fungi would be a better choice for inoculation into a bio-trickling filter because of the quickly degradation of H₂S and rapid recovery under shut-down experiment. This is the first study attempting to combine bacteria and fungi for removal of H₂S in a bio-trickling filter.     

Synthesis of CuO nanoparticles through green route using Citrus limon juice and its application as nanosorbent for Cr(VI) remediation: Process optimization with RSM and ANN-GA based model

In present investigation, an attempt has been made for the synthesis of cupric oxide nanoparticles (CuONPs) through a green route by utilizing lemon juice extract as a bioreductant. The synthesized CuONPs were characterized through UV–visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The CuONPs were utilized for Cr(VI) removal from water through adsorption method in batch mode at different initial Cr(VI) concentration, pH, temperature and CuONPs dosage. The maximum uptake capacity of CuONPs was found to be 16.63 mg of Cr(VI)/g at pH 4.0. Implementation of response surface methodology (RSM) followed by artificial neural network hybridized with genetic algorithm (ANN-GA) approach has resulted maximum Cr(VI) adsorption of 98.8% under the optimized conditions of initial metal concentration 22.5 mg/L, pH 3.81, CuONPs dose 1.28 g/L and temperature 37.1 °C. Under optimum conditions, adsorption isotherm study was conducted, which showed that the fitness of experimental data was well achieved with Langmuir isotherm model illustrating monolayer pattern of adsorption. Thermodynamic study revealed that the process was spontaneous and endothermic in nature, while adsorption kinetics was best explained by pseudo-second order kinetic model.     

Preparation of Co–MgO mixed oxide nanocatalysts for low temperature CO oxidation: Optimization of preparation conditions

In this study, a series of Co–MgO mixed oxides (30 wt.% Co) were prepared by co-precipitation method and employed as catalyst in low temperature CO oxidation reaction. The preparation conditions were optimized by the Taguchi method of experimental design to synthesize a sample with high catalytic performance toward CO oxidation reaction. The effects of four variables, pH of solution, aging temperature, aging time and molarity of precursor solution at three levels were investigated. The optimized sample was characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption of oxygen (O₂-TPD), N₂ adsorption/desorption, thermal gravimetric and differential thermal analysis (TGA/DTA), and transmission electron microscopy (TEM) techniques. The results revealed that the optimized sample showed a mesoporous structure with a narrow pore size distribution centered in the range of 7–17 nm and particle size about 5.5 nm. It was found that the molarity of solution and aging time had the most influence on the CO conversion, respectively. The catalytic results showed that the highest CO conversion obtained from samples synthesized by Taguchi orthogonal array was about 90% at 200 °C, while the CO conversion for optimized sample was 95%. In addition, the effect of operational conditions was studied over optimized sample.     

Growing Carbon Nanotube on Aluminum Oxides: An Inherently Safe Approach for Environmental Applications

Using micron-sized Al₂O₃ particles as carriers to grow carbon nanotubes (CNTs) under 700°C atmosphere of methane and hydrogen after pre-planted catalysts of Fe–Ni nanoparticles, those composite CNTs (CCNTs) have demonstrated several unique properties compared to CNTs—medium specific surface area and zeta potential, high adsorption capacity for metal ions, high recovery rate by acids, low decomposition heat for exothermal reaction, and so on. The adsorption behaviours of Pb²⁺, Cu²⁺ and Cd²⁺ in aqueous solutions by CCNTs are in good agreement with the Langmuir adsorption isotherm and second order kinetic model with maximum individual adsorption capacities of 67.11, 26.59 and 8.89 mg g⁻¹. The individual and competitive adsorption behaviours indicated that the preference order of adsorption were Pb²⁺ > Cu²⁺ > Cd²⁺ for aluminum oxides, activated carbon, commercial CNTs, and CCNTs as well as other researchers’ CNTs. We suggest that future development of CNTs to combine with metals and/or other materials, such as TiO₂, should consider attached to carriers or surface in order to avoid concerns on environment, health and safety. Thus, growing CNTs on Al₂O₃ particles to form CCNTs is an inherently safe approach for many promising environmental applications.     

Removal of a cationic bisbiguanide using Functionalized Activated Carbons (FACs)

Functionalized Granular Activated Carbons (FACs) are used as adsorbents for treating pharmaceutical wastewaters containing Chlorhexidine Gluconate. Chemical modifications of Granular Activated Carbons (GACs) using functionalizing agents like HCl and HF produce FACs. The adsorption capacity of each of FAC-HCl and FAC-HF is found to be higher than GAC. The modelled maximum adsorption capacity for FAC-HCl is 1.02 g/g of adsorbent, 3.49 g/g of adsorbent for FAC-HF and 0.0682 g/g of adsorbent for GAC. This is mainly due to the additional chemisorptions by surface complexation at the functionalized surface sites of the modified GACs. This is also supported by the well-known pseudo-second-order kinetic model. Formation of surface complexes with the functional groups and weakly polar Chlorhexidine Gluconate is well supported by the physical characterization using Energy dispersive X-ray spectroscopy (EDAX), Brunner–Emmett–Teller (BET) test and Fourier Transform Infrared spectroscopy (FTIR) analysis after adsorption. The adsorption capacity of GAC and the FACs increases in the order of FAC-HF > FAC-HCl > GAC conforming to the proportion of the total acidity of the carbon surfaces. Intra-particle diffusion is not the sole rate-controlling factor. An agreement to pseudo-second-order kinetic model, Elovich kinetic model and Boyd's film diffusion model proves that chemisorption is the rate-controlling parameter in this adsorption study.     

Low-dose irradiation by electron beam for the treatment of high-SOx flue gas on a semi-pilot scale—Consideration of by-product quality and approach to clean technology

Attention has been focused on the treatment of lignite-fired flue gas in order to use lignite in an environmentally friendly way – (i) low-CO₂ emission, (ii) production of a valuable by-product, (iii) no discharge of wastewater, (iv) direct removal of SO₃ (strong toxicity), and (v) treatment of high SO₂ concentration. Based on these criteria, electron beam irradiation with ammonia injection was tested on a semi-pilot scale: 800 Nm³ h^?1 flow rate, 5500 ppm SO₂, 70 ppm NO_x, 22% flue gas moisture, and 75–80 °C at the reactor outlet.As an energy-saving measure, a low dose (5 kGy) of irradiation was applied: the problem lay in the by-product quality. It is considered that (NH₄)₂SO₃ and NH₄HSO₃ produced by thermal reactions are oxidized to form (NH₄)₂SO₄ (fertilizer) by an electron beam. However, not all reactions were complete because the by-product contained small amounts of H₂SO₄ and NH₂SO₃NH₄ (herbicide), so a vegetable pot test was performed to study the by-product quality: no adverse effect was observed. It is inferred from the pot test that slightly acidic soil may protect vegetables from disease and a small amount of NH₂SO₃NH₄ probably affects woody species and not herbaceous species.It is concluded that the electron beam system is noted as a multi-component pollution control process (removal of NO_x, SO₃, SO₂ and dioxins) and this system will contribute to environmentally friendly use of lignite as well as agricultural productivity via fertilizer supply.     

Thermal characterization of fly ash from one municipal solid waste incinerator (MSWI) in Shanghai

This study aims to develop a methodology for the thermal characterization of MSWI fly ash. We performed TGA–DTA and component variation analysis, microstructure transfer of sintered fly ash, as well as leaching toxicity, volatilization ratio and specification transformation of heavy metals as a function of temperature. It is found that content of crystal phases first increases between room temperature and 800 °C and then decreases between 800 °C and 1200 °C, while that of glass phases registers a reverse trend. Fly ash registers a SiO₂–Al₂O₃–metal oxides system and its content of glass phases is around 57%. Increase of sintering temperature between 600 °C and 1200 °C is conducive to the reduction of soluble As, Cd, Cu, Hg, Pb, Ni and Zn, while content of soluble Cr increases as temperature rises from 800 °C to 1200 °C.     

Hydrogen sulphide removal from landfill gas

Control of odours should be considered to be a fundamental issue in order to site, design and manage sanitary landfills. With regard to construction and demolition (C&;D) debris, landfilling was the mainly adopted solution in many European Countries; in particular, gypsum drywalls can produce high concentrations of hydrogen sulphide (H₂S) in landfill gas ranging from 7 ppm to 100 ppm. In some cases also dangerous concentrations until to 12,000 ppm were detected. In this paper H₂S removal efficiency in a lab-scale vertical packed scrubber was investigated. Hydrogen sulphide abatement was evaluated for inlet H₂S concentrations of 1000–100–10 ppm, adjusting scrubbing liquid pH in the range 9–12.5 by means of caustic soda (NaOH 2N solution). Moreover, best operating conditions for the system were defined as well as H₂S abatement along the tower and liquid recirculation effectiveness in case of inlet H₂S concentration of 10 ppm (typical odour concentration). Results showed that pH of 11.5 in scrubbing liquid could be considered the best value for removal of different inlet H₂S concentrations, also taking into account parasitical consumption of NaOH due to CO₂ absorption. Moreover, in case of continuous working of the system at H₂S concentration of 10 ppm, strong removal efficiency was already obtained with a packed bed height of about 70 cm. Significant performances were ensured after 1 h of constant activity, consuming about 3 ml of soda per cubic meter of polluted air. Subsequently liquid blowdown was necessary.     

Partial nitritation of landfill leachate with varying influent composition under intermittent aeration conditions

The start-up and operation of a partial nitritation sequencing batch reactor for the treatment of landfill leachate were carried out on intermittent aeration mode. Partial nitrite accumulation was established in 15 days after the mode was changed from continuous aeration to intermittent aeration. Despite the varying influent composition, partial nitritation could be maintained by adjusting the hydraulic retention time (HRT) and the air flow rate. An increase in the air flow rate together with a decrease in air off duration can improve the partial nitritation capacity and eventually result in the development of granular sludge with fine diameters. A nitrogen loading rate of 0.71 ± 0.14 kg/m³/d and a COD removal rate of 2.21 ± 0.13 kg/m³/d were achieved under the conditions of an air flow rate of 19.36 ± 1.71 m³ air/m³/h and an air on/off duration of 1.5 min/0.7 min. When the ratio of total air flux (TAF) to the influent loading rate (ILR) was controlled at the range of 163–256 m³ air/kg COD, a stable effluent NO₃^?–N/NO_x^?–N (NO₂^?–N plus NO₃^?–N) ratio below 13% was achieved. Interestingly, the effluent pH was found to be a good indicator of the effluent NO₂^?–N/NH₄⁺–N ratio, which is an essential parameter for a subsequent anaerobic ammonium oxidation (Anammox) reactor.     

Achieving stable partial nitritation using endpoint pH control in an SBR treating landfill leachate

The feasibility of using endpoint pH control to achieve stable partial nitritation (PN) in an SBR for landfill leachate treatment was investigated. By imposing a fixed-time anoxia followed by variable-time aeration in an SBR cycle, successful partial nitritation was maintained for 182 days at a nitrogen loading rate of 0.30–0.89 kg/m³/day. The effluent NO₂⁻-N/NH₄⁺-N ratio and the effluent NO₃⁻-N concentration were 1.30 ± 0.22 and 16 ± 9 mg/L, respectively. High free ammonia (FA) and low dissolved oxygen (DO) concentrations were inhibition factors of nitrate formation. The termination of aeration at a suitable endpoint pH was the key to achieve an effluent NO₂⁻-N/NH₄⁺-N ratio close to the stoichiometric value. This endpoint pH control strategy represents practical potentials in the engineered application of combined PN–ANAMMOX processes.